Techniques for bus interval timing management in a USB extension system

Abstract

Techniques for generating bus interval messages by a downstream USB extension device in a USB extension environment are disclosed. The downstream USB extension device transmits a first outgoing bus interval message in response to receiving a first incoming bus interval message at a first time. An expected time of receipt of a second incoming bus interval message is determined based on the first time. The downstream USB extension device transmits a second outgoing bus interval message at a second time based on a difference between the reception time and the expected time of receipt if the second incoming bus interval message has been received at a reception time before the expected time of receipt. The downstream USB extension device transmits the second outgoing bus interval message at the expected time of receipt if the second incoming bus interval message has not been received before the expected time of receipt.

The embodiments of the invention in which an exclusive property or privilege is claimed are defined as follows: 
     
       1. A method for generating bus interval messages by a downstream USB extension device in a USB extension environment, the method comprising:
 transmitting, by the downstream USB extension device via a USB downstream facing port, a first outgoing bus interval message in response to receiving a first incoming bus interval message from an upstream USB extension device via an extension medium at a first time; 
 determining, by the downstream USB extension device, an expected time of receipt of a second incoming bus interval message based on the first time; 
 in response to determining that the second incoming bus interval message has been received at a reception time that is before the expected time of receipt, transmitting, by the downstream USB extension device via the USB downstream facing port, a second outgoing bus interval message at a second time based on a difference between the reception time and the expected time of receipt; and 
 in response to determining that the second incoming bus interval message has not been received before the expected time of receipt, transmitting, by the downstream USB extension device via the USB downstream facing port, the second outgoing bus interval message at the expected time of receipt. 
 
     
     
       2. The method of  claim 1 , wherein transmitting the second outgoing bus interval message at the second time based on the difference between the reception time and the expected time of receipt includes:
 in response to determining that the reception time is between the expected time of receipt and an earlier soft threshold time, using the reception time as the second time; 
 wherein the earlier soft threshold time is before the expected time of receipt. 
 
     
     
       3. The method of  claim 2 , further comprising:
 setting a second expected time of receipt for a third incoming bus interval message as a predetermined amount of time after the reception time. 
 
     
     
       4. The method of  claim 1 , wherein transmitting the second outgoing bus interval message at the second time based on the difference between the reception time and the expected time of receipt includes:
 in response to determining that the reception time is between an earlier soft threshold time and an earlier hard threshold time, using the earlier soft threshold time as the second time; 
 wherein the earlier soft threshold time is before the expected time of receipt, and the earlier hard threshold time is before the earlier soft threshold time. 
 
     
     
       5. The method of  claim 4 , further comprising:
 setting a second expected time of receipt for a third incoming bus interval message as a predetermined amount of time after the earlier soft threshold time. 
 
     
     
       6. The method of  claim 1 , wherein transmitting the second outgoing bus interval message at the second time based on the difference between the reception time and the expected time of receipt includes:
 in response to determining that the reception time is earlier than an earlier hard threshold time, using the expected time of receipt as the second time. 
 
     
     
       7. The method of  claim 1 , further comprising:
 in response to determining that the second incoming bus interval message has been received at a reception time that is between the expected time of receipt and a later soft threshold time, setting a second expected time of receipt for a third incoming bus interval message as a predetermined amount of time after the reception time; 
 wherein the later soft threshold time is after the expected time of receipt. 
 
     
     
       8. The method of  claim 1 , further comprising:
 in response to determining that the second incoming bus interval message has been received at a reception time that is between a later soft threshold time and a later hard threshold time, setting a second expected time of receipt for a third incoming bus interval message as a predetermined amount of time after the later soft threshold time; 
 wherein the later soft threshold time is after the expected time of receipt; and 
 wherein the later hard threshold time is after the later soft threshold time. 
 
     
     
       9. The method of  claim 1 , further comprising:
 in response to determining that the second incoming bus interval message has not been received by a later hard threshold time, setting a second expected time of receipt for a third incoming bus interval message as a predetermined amount of time after the expected time of receipt. 
 
     
     
       10. A downstream USB extension device configured to perform actions comprising:
 transmitting, by the downstream USB extension device via a USB downstream facing port, a first outgoing bus interval message in response to receiving a first incoming bus interval message from an upstream USB extension device via an extension medium at a first time; 
 determining, by the downstream USB extension device, an expected time of receipt of a second incoming bus interval message based on the first time; 
 in response to determining that the second incoming bus interval message has been received at a reception time that is before the expected time of receipt, transmitting, by the downstream USB extension device via the USB downstream facing port, a second outgoing bus interval message at a second time based on a difference between the reception time and the expected time of receipt; and 
 in response to determining that the second incoming bus interval message has not been received before the expected time of receipt, transmitting, by the downstream USB extension device via the USB downstream facing port, the second outgoing bus interval message at the expected time of receipt. 
 
     
     
       11. The downstream USB extension device of  claim 10 , wherein transmitting the second outgoing bus interval message at the second time based on the difference between the reception time and the expected time of receipt includes:
 in response to determining that the reception time is between the expected time of receipt and an earlier soft threshold time, using the reception time as the second time; 
 wherein the earlier soft threshold time is before the expected time of receipt. 
 
     
     
       12. The downstream USB extension device of  claim 11 , wherein the actions further comprise:
 setting a second expected time of receipt for a third incoming bus interval message as a predetermined amount of time after the reception time. 
 
     
     
       13. The downstream USB extension device of  claim 10 , wherein transmitting the second outgoing bus interval message at the second time based on the difference between the reception time and the expected time of receipt includes:
 in response to determining that the reception time is between an earlier soft threshold time and an earlier hard threshold time, using the earlier soft threshold time as the second time; 
 wherein the earlier soft threshold time is before the expected time of receipt, and the earlier hard threshold time is before the earlier soft threshold time. 
 
     
     
       14. The downstream USB extension device of  claim 13 , wherein the actions further comprise:
 setting a second expected time of receipt for a third incoming bus interval message as a predetermined amount of time after the earlier soft threshold time. 
 
     
     
       15. The downstream USB extension device of  claim 10 , wherein transmitting the second outgoing bus interval message at the second time based on the difference between the reception time and the expected time of receipt includes:
 in response to determining that the reception time is earlier than an earlier hard threshold time, using the expected time of receipt as the second time. 
 
     
     
       16. The downstream USB extension device of  claim 10 , wherein the actions further comprise:
 in response to determining that the second incoming bus interval message has been received at a reception time that is between the expected time of receipt and a later soft threshold time, setting a second expected time of receipt for a third incoming bus interval message as a predetermined amount of time after the reception time; 
 wherein the later soft threshold time is after the expected time of receipt. 
 
     
     
       17. The downstream USB extension device of  claim 10 , wherein the actions further comprise:
 in response to determining that the second incoming bus interval message has been received at a reception time that is between a later soft threshold time and a later hard threshold time, setting a second expected time of receipt for a third incoming bus interval message as a predetermined amount of time after the later soft threshold time; 
 wherein the later soft threshold time is after the expected time of receipt; and 
 wherein the later hard threshold time is after the later soft threshold time. 
 
     
     
       18. The downstream USB extension device of  claim 10 , wherein the actions further comprise:
 in response to determining that the second incoming bus interval message has not been received by a later hard threshold time, setting a second expected time of receipt for a third incoming bus interval message as a predetermined amount of time after the expected time of receipt. 
 
     
     
       19. A system, comprising:
 an extension medium; and 
 a downstream USB extension device communicatively coupled to the extension medium and configured to perform actions comprising:
 transmitting, by the downstream USB extension device via a USB downstream facing port, a first outgoing bus interval message in response to receiving a first incoming bus interval message from an upstream USB extension device via the extension medium at a first time; 
 determining, by the downstream USB extension device, an expected time of receipt of a second incoming bus interval message based on the first time; 
 in response to determining that the second incoming bus interval message has been received at a reception time that is before the expected time of receipt, transmitting, by the downstream USB extension device via the USB downstream facing port, a second outgoing bus interval message at a second time based on a difference between the reception time and the expected time of receipt; and 
 in response to determining that the second incoming bus interval message has not been received before the expected time of receipt, transmitting, by the downstream USB extension device via the USB downstream facing port, the second outgoing bus interval message at the expected time of receipt. 
 
 
     
     
       20. The system of  claim 19 , wherein the extension medium includes a copper cable, a fiber-optic cable, or a wireless medium.